In recent years, it has become possible to determine a disease of the heart, brain, etc., by observing various functional images. For example, when cerebral ischemia diseases, such as acute-phase cerebral infarction, transient ischemic attack and chronic head-and-neck angiostenosis, are to be diagnosed, cerebral circulation metabolism amounts are evaluated based on perfusion images as two-dimensional or three-dimensional images acquired by various kinds of medical diagnostic imaging apparatuses.
As concrete analysis indices of the cerebral circulation metabolism amounts, there are such kinds of indices as a cerebral blood flow CBF [ml/100 g/min], a cerebral blood volume CBV [ml/100 g], a cerebral oxygen extraction fraction OEF [%], and a cerebral metabolic rate of oxygen CMRO2 [ml/100 g/min]. CBF is an abbreviation for Cerebral Blood Flow, and CBV for Cerebral Blood Volume. OEF is an abbreviation for Cerebral Oxygen Extraction Fraction, and CMRO2 for Cerebral Metabolic Rate of Oxygen.
In usual cases, a doctor observes magnitudes of these analysis indices in an ischemia region on a plurality of functional images, thereby comprehensively judging a severity of cerebral circulation metabolism, and deciding on courses of treatment.
Of the respective analysis indices, the magnitudes of the cerebral blood flow CBF and cerebral blood volume CBV are observed on perfusion images. Incidentally, the perfusion images are obtained from, for example, an X-ray CT (computed tomography) apparatus, an MRI (magnetic resonance imaging) apparatus, a SPECT (single photon emission CT) apparatus or a PET (positron emission tomography) apparatus.
In addition, of the respective analysis indices, the magnitudes of the cerebral oxygen extraction fraction OEF and cerebral metabolic rate of oxygen CMRO2 are observed on PET images which are obtained by, in particular, the PET apparatus.
As one index serving as a criterion for the doctor to determine the severity of the cerebral circulation metabolism after the observation of the magnitude of each analysis index, there is a typical concept of severity determination, which is called stage classification of Powers. The Powers' stage classification is comprised of indices which classify the stage of severity into three stages, by a combination of magnitudes of the above-described various analysis indices. Specifically, in these indices, as illustrated in FIG. 11, the severity of the cerebral circulation metabolism is classified into stages I, II and III, based on the magnitudes of the above-described four analysis indices (CBF, CBV, OEF, CMRO2). In general, stage III is regarded as an untreatable state because of infarction (brain cell necrosis). Stage II corresponds to a state which is called an ischemic penumbra (reversible tissue impairment), and is regarded as a state in which normalization is possible by blood flow recovery by medical treatment. The ratio of a remaining ischemic penumbra region is important in deciding on courses of treatment.
A concrete method of stage classification is described with reference to FIG. 12. In an example shown in FIG. 12, the cerebral blood flow CBF of the diseased side (the side on which cerebral ischemia occurs) decreases, the cerebral blood volume CBV increases, the cerebral oxygen extraction fraction OEF increases and the cerebral metabolic rate of oxygen CMRO2 decreases, and thus this example corresponds to stage III and is regarded as a state of brain cell necrosis.
However, in the method of stage classification as described above, determination is not possible unless thorough consideration is given to which stage the combination of the magnitudes of the four analysis indices corresponds to. Thus, there is a possibility that time is consumed for determination, or erroneous determination is made.
In addition, in an actual clinical diagnosis, such a case occurs that a combination, which corresponds to none of the stages, occurs. In such a case, there is concern over what diagnosis result should be given.
Furthermore, when all functional images have failed to be obtained, or, conversely, when a plurality of functional images have been obtained from different medical diagnostic imaging apparatuses with respect to one analysis index, a subjective judgment tends to be given concerning information which is in excess or insufficient, and it is possible that a proper diagnosis result cannot be given.
The object is to provide a stage determination support system which can display a possibility that a disease corresponds to each of stages, based on obtained functional images, and can support stage determination by a user.